1. Field of the Invention
This invention relates generally to materials handling equipment such as lift trucks and more particularly to mast reeving systems for hydraulic hose lines.
2. Precedent for the Invention
Materials handling equipment and in particular, lift trucks, have constituted specialized application vehicles. Lift trucks were designed to raise, lower and carry materials in a cantilevered arrangement while at the same time, maneuver into extremely tight quarters.
To optimize storage space, warehouse racks were often stacked high and aisles between the racks were narrow. Typical loads were transported to and from warehouses in vehicles ranging from railroad box cars to semi trailers, trucks, vans and smaller vehicles, all of which presented challenging loading and unloading conditions for a typical lift truck. Accordingly, lift trucks have been designed for operating in varied conditions ranging from narrow aisles of high bay storage racks to inside low clearance box cars, semi-trailers and other challenging environments.
Safe operation of lift trucks has been a paramount design consideration. A principal factor in assuring safe lift truck operation in conjunction with load lifting, maneuvering and transport has been to assure operator visibility.
Lift trucks have been traditionally configured with a generally upright forward mast assembly which supported a moveable load carriage. Suitable load engaging attachments, such as forks, were mounted to the carriage. The carriage itself was raised or lowered relative to the mast assembly for lifting a load, for lowering the load to a transport position and for placement of the load in its desired location.
Mast assemblies included at least one rail to which the carriage was mounted for load engagement. Both the carriage and the rail were preferably moveable in a vertical plane, with movement between the carriage and the rail being effected by a hydraulic cylinder and a pair of chains, anchored at one end to the carriage and extending over sheaves.
In order to provide high lift, i.e. the capability of removing and placing loads in high storage racks, lift truck mast assemblies were provided with nested multiple rail stages. For example, lift truck masts with two rails (simplex and duplex), three rails (triplex), and four rails (quadplex) have been employed. Hydraulic cylinders and chains have been employed to effect progressive movement of the plurality of rail stages.
Significant lift truck design considerations related to extending hydraulic hose lines to the carriage elevating cylinder as well as to hydraulic actuated accessories associated with the carriage, such as side shifters, clamps, pushers, etc. It was not uncommon for four or more hydraulic hose lines to be employed for a carriage and accessories.
Safe operation mandated that the hoses not become entangled with one another or with the chains during travel of the mast rails and carriage.
One design approach was the employment of external reeving with hydraulic hose being coiled about large take up reels. The fluid supply line extended to the hub of the reels with the hose being uncoiled as needed to reach the carriage elevating cylinder and carriage accessories. External reeving generally required that hoses extend from the reels, which were mounted to the outside of the outer rail, along the outside of the mast assembly. There was an implicit danger of exposing hose lines to contact with workplace hazards e.g. racks, columns, etc, and/or entangling the lines. Further, oil seals at the reels required frequent inspection and servicing.
Internal reeving, on the other hand, employed a plurality of upper and lower sheaves on adjacent rails. The sheaves rotated about axes which were transverse, i.e., side to side, and were laterally spaced from one another along their axes across the width of the vehicle to avoid entanglement of adjacent lines. The hose runs from each upper sheave to its respective lower sheave were vertical. Unfortunately, the successive vertical hose runs obstructed the operator's forward view, which was framed by the inner rail. Decreased operator visibility was a significant drawback and a major safety consideration with internal reeving.